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    <!-- 利用递归求100的阶乘

100 * 99 * 98 * 97 * … * 1 = ? -->

    <script>
      function fn(num) {
        if (num == 1) {
          return num * 1;
        }
        return num * fn(num - 1);
      }
      var res = fn(100);
      console.log(res);
    </script>
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